1. Field of the Invention
The present invention relates generally to a gas turbine moving blade and more particularly to a gas turbine moving blade which is improved with regard to its blade and platform cooling structure so as to prevent occurrence of cracks due to thermal stresses caused by temperature changes during gas turbine starts and stops, or caused by high temperature combustion gas.
2. Description of the Prior Art
In FIG. 14, which is a cross sectional view of a representative first stage moving blade of a prior art gas turbine, numeral 20 designates the moving blade, numeral 21 designates a blade root portion and numeral 22 designates a platform. In the blade root portion 21, there are provided cooling passages 23, 24, 25, 26, which are independent of each other. The cooling passage 23 is a passage on a blade leading edge side to communicate with a cooling passage 23a provided in a blade leading edge portion. Cooling air represented by arrow 40 flows into the cooling passage 23 from a turbine rotor side to flow through the cooling passage 23a and to flow out of a blade tip portion for cooling the blade leading edge portion and, at the same time, to flow out of cooling holes 29 for effecting a shower head film cooling of the blade leading edge portion. Cooling air represented by arrow 41 flows into the cooling passage 24 to flow through a cooling passage 24a provided in the blade, and then turns at the blade tip portion to flow through a cooling passage 24b, and turns again at a blade base portion to flow through a cooling passage 24c, and then flow out of the blade tip portion. In this process of the flow, the cooling air represented by arrow 41 cools a blade interior and, at the same time, flows out of cooling holes, to be described later with respect to FIG. 15, onto a blade surface for effecting a film cooling thereof.
Cooling air represented by arrow 42 entering the cooling passage 25, and cooling air represented by arrow 43 entering the cooling passage 26, join together to flow through a cooling passage 25a, then turn at the blade tip portion to flow through a cooling passage 25b, and turn again at the blade base portion to flow through a cooling passage 25c. In this process of the flow, the cooling air represented by arrows 42, 43 cools the blade interior and, at the same time, flows out of cooling holes, to be described later with respect to FIG. 15, onto the blade surface for effecting the film cooling thereof. A remaining portion of the cooling air represented by arrows 42, 43 flows out of cooling holes 28 of a blade trailing edge 27 for effecting a pin fin cooling of a blade trailing edge portion.
In FIG. 15, which is a cross sectional view taken on line Bxe2x80x94B of FIG. 14, a portion of the cooling air flowing through the cooling passage 23a in the blade leading edge portion flows out of the blade through the cooling holes 29 for effecting the shower head film cooling of the blade leading edge portion. Also, a portion of the cooling air flowing through the cooling passage 24c flows outside obliquely through cooling holes 30 for effecting the film cooling of the blade surface. Likewise, a portion of the cooling air flowing through the cooling passage 25c flows outside obliquely through cooling holes 31 for effecting the film cooling of the blade trailing edge portion. It is to be noted that although the cooling holes 29, 30, 31 only are illustrated, there are actually provided a multiplicity of cooling holes other than the mentioned three kinds of the cooling holes 29, 30, 31.
In FIGS. 16(a) and 16(b), which are explanatory plan views of a cooling structure of the platform 22, FIG. 16(a) shows an example to cool a front portion, or a blade leading edge side portion, of the platform 22 as well as to cool both side portions, or blade ventral and dorsal side portions, of the platform 22. And FIG. 16(b) shows another example to cool upper surface portions of both of the side portions of the platform 22 in addition to the cooled portions of FIG. 16(a). In FIG. 16(a), there are bored cooling passages 50a, 50b in the front portion and both of the side end portions of the platform 22 so as to communicate with the cooling passage 23 of the leading edge portion of the moving blade 20. Cooling air represented by arrows 72a, 72b flows through the cooling passages 50b, 50a, respectively, for cooling the front portion and both of the side portions of the platform 22, and flows out through a rear portion, or a blade trailing edge side portion, of the platform 22 as air represented by arrows 72c, 72d. 
In FIG. 16(b), in addition to the cooling passages 50a, 50b of FIG. 16(a), there are provided a plurality of cooling holes 51a, 51b, respectively, in both of the side portions of the platform 22 so as to open at an upper surface of the platform 22. These cooling holes 51a, 51b communicate with one or more of the cooling passages leading to the interior of the moving blade 20, so that cooling air flows through the cooling holes 51a, 51b to flow out onto the upper surface of the platform 22 and cool both of the side portions of the platform 22. Thus, in the gas turbine moving blade, the moving blade 20 as well as the platform 22 are cooled as described with respect to FIGS. 14 to 16(b), so that thermal influences resulting from high temperature combustion gas are mitigated.
In FIGS. 17(a)-17(c), which show an example of a second stage moving blade in the prior art, FIG. 17(a) is a cross sectional view thereof, FIG. 17(b) is a cross sectional view taken on line Fxe2x80x94F of FIG. 17(a) and FIG. 17(c) is a cross sectional view taken on line Gxe2x80x94G of FIG. 17(a). In FIGS. 17(a) and (b), numeral 180 designates the second stage moving blade, numeral 181 designates a blade root portion and numeral 182 designates a platform. In the blade root portion 181, there are provided cooling passages 183, 184, 185, which are independent of each other. The cooling passage 183 is a passage on a blade leading edge side to communicate with a cooling passage 183a provided in a blade leading edge portion. Cooling air represented by arrow 190 flows into the cooling passage 183 from a turbine rotor side to flow through the cooling passage 183a for cooling the blade leading edge portion and to flow outside through a blade tip portion. Cooling air represented by arrow 191 flows into the cooling passage 184 to flow through a cooling passage 184a provided in the blade, then turns at the blade tip portion to flow through a cooling passage 184b, and turns again inwardly toward a blade base portion. In the blade base portion, the cooling air represented by arrow 191, and cooling air represented by arrow 192 flowing through the cooling passage 185, join together and flow into a cooling passage 184c. In the cooling passage 184c, the cooling air represented by arrows 191, 192 flows between pin fms 195 for enhancing the cooling effect, and flows outside through slots 186 provided in a blade trailing edge as well as through a hole of the blade tip portion. In this process of the cooling air flow, the blade is cooled.
In FIG. 17(c), there is provided a blade tip thinned portion 187 along each of blade tip edge portions of the moving blade 180 so as to function as a seal of air leaking toward blade rear stages from the blade tip. Numeral 188 designates a plug, which plugs up openings provided for working purposes when the moving blade 180 is being manufactured. In the second stage moving blade 180 as so constructed, the cooling air is led into the interior of the blade, so that thermal influences resulting from high temperature combustion gas are mitigated.
As mentioned above, in the gas turbine moving blade, the blade and the platform are cooled by flowing the cooling air, and elevation of metal temperature due to the high temperature combustion gas is suppressed. While there is a large difference in mass between the platform and a blade profile portion of the gas turbine moving blade, the platform and the blade profile portion are cooled by the cooling air during a gas turbine steady operation time, and there occurs no large temperature difference between the platform and the blade profile portion, so that thermal stress influences caused by the temperature difference are also small. However, during an unsteady time during stoppage of the gas turbine, while the blade profile portion, which is of a thin shape, has been previously cooled, the platform, which is of a larger mass, is cooled slowly, and this causes a large temperature difference between the the platform and the blade profile portion, which results in large thermal stresses.
If large thermal stresses occur between the blade profile portion and the platform, as mentioned above, cracks may arise easily, especially at a portion where there is the severest thermal influence; that is, at blade hub portions where the blade and the platform join together at the blade leading edge and trailing edge sides. Also, cracks are likely to arise at other portions where there are thermal stress influences; that is, at the cooling holes of the blade trailing edge, the blade tip thinned portion and the like.
The cracks of the mentioned portions are caused by a combination of creep ruptures caused by high temperature and high stress repeated because of long time operations, and fatigue failures caused by repeated stresses due to operation starts and stops. In order to avoid such cracks, it is necessary to reduce the temperature and thermal stresses as much as possible at portions where stress concentrations are caused (i.e. blade and platform fitting portions at the blade leading edge and trailing edge portions).
In view of the problems in the prior art, therefore, it is an object of the present invention to provide a gas turbine moving blade which is improved with regard to structural portions of the blade and platform, which are prone to be influenced by thermal stresses, especially blade and platform fitting portions and blade trailing edge cooling holes. It is another object to provide a gas turbine moving blade which is improved with regard to cooling structures of a blade tip portion, and platform front and rear end portions, so that cracks caused by thermal stresses due to temperature differences may be suppressed and life and reliability of the blade may be enhanced.
In order to achieve the mentioned objects, the present invention provides the following (1) to (11):
(1) A gas turbine moving blade comprising a platform and a blade fitting portion where a blade is fitted to the platform, A blade cooling passage is provided in the blade, a platform cooling passage is provided in the platform, and cooling air blow holes are provided in and around the blade so that the blade may be cooled by cooling air flowing through the blade cooling passage, flowing through the platform cooling passage, and flowing out of the blade through the cooling air blow holes. Also provided is a recessed portion, having a smooth curved surface and extending in a direction orthogonal to a turbine axial direction. The recessed portion is in an end face portion of a rear side portion of the platform near the blade fitting portion on a blade trailing edge side. The blade fitting portion is formed with a fillet exterior having a curved surface. The cooling air blow holes are provided in a blade trailing edge and include a hole provided in a blade hub portion positioned at a lowermost end of the cooling air blow holes. This hole in the blade hub portion has a hole cross sectional area larger than that of each of the other cooling air blow holes provided above the hole in the blade hub portion.
(2) A gas turbine moving blade as mentioned in (1) above, characterized in that there is applied a coating of a heat resistant material to the blade and platform so that the blade fitting portions of the blade leading edge and trailing edge portions are provided with a coating that is thicker than the coating on other portions of the blade, and portions of the platform near and around the blade leading edge and trailing edge portions are provided with a coating that is thinner than the coating on other portions of the platform.
(3) A gas turbine moving blade as mentioned in (1) above, characterized in that the curved surface of the fillet exterior defines an elliptical curve.
(4) A gas turbine moving blade as mentioned in (1) above, characterized in that the platform cooling passage is connected with a platform cooling air supply system, and there are provided in the platform cooling air supply system an opening/closing valve for opening and closing the platform cooling air supply system. Also, provided is a control unit for controlling the opening/closing valve so as to be closed while a gas turbine is being operated and to be opened for a predetermined time when the gas turbine is being stopped.
(5) A gas turbine moving blade as mentioned in (1) above, further comprising a shank portion for fixing the platform. The shank portion has an elongated shape having a height (H) in the turbine radial direction which is larger than a width (W) of the shank portion in a turbine rotational direction (H greater than W).
(6) A gas turbine moving blade comprising a platform and a blade fitting portion where a blade is fitted to the platform. A blade serpentine cooling passage is provided in the blade, a platform cooling passage is provided in each of blade ventral and dorsal side end portions of the platform, and cooling air blow holes are provided in and around the blade so that the blade may be cooled by cooling air flowing through the blade serpentine cooling passage, flowing through the platform cooling passage, and flowing out of the blade through the cooling air blow holes. The blade serpentine cooling passage comprises two flow paths constructed such that cooling air entering a central portion of a blade root portion flows toward the blade leading edge and trailing edge sides. The blade fitting portion has an exterior with a curved surface. There is provided a recessed portion, extending in a direction orthogonal to a turbine axial direction, in an end face portion of each of front side and rear side portions of the platform near the blade fitting portions on the blade leading edge and trailing edge sides. The cooling air blow holes include a plurality of cooling holes provided in the platform, with the cooling holes being arranged along the platform cooling passage on the blade dorsal side, and each having one end communicating with the platform cooling passage on the blade dorsal side and another end opening at an end face on the blade dorsal side of the platform.
(7) A gas turbine moving blade as mentioned in (6) above, characterized in that the curved surface of the exterior of each of the blade fitting portions on the blade leading edge and trailing edge sides comprises a combination of a linear portion and a curved portion.
(8) A gas turbine moving blade as mentioned in (6) above, further comprising a blade tip thinned portion provided only at a blade tip edge portion on the blade dorsal side, and a plug of a circular shape provided in a blade tip portion.
(9) A gas turbine moving blade as mentioned in any one of (6) to (8) above, further comprising a shank portion for fixing the platform. The shank portion has an elongated shape having a height (H) in the turbine radial direction which is larger than a width (W) of the shank portion in a turbine rotational direction (H greater than W).
(10) A gas turbine moving blade comprising a platform and a blade fitting portion where a blade is fitted to the platform. A blade serpentine cooling passage is provided in the blade, a platform cooling passage is provided in each of blade ventral and dorsal side end portions of the platform, and cooling air blow holes are provided in and around the blade so that the blade may be cooled by cooling air flowing through the blade serpentine cooling passage, flowing through the platform cooling passage and flowing out of the blade through the cooling air blow holes. The blade serpentine cooling passage comprises a flow path constructed such that cooling air entering a central portion of a blade root portion flows toward a blade trailing edge side. The blade fitting portion has an exterior with a curved surface. There is provided a recessed portion, extending in a direction orthogonal to a turbine axial direction, in an end face portion of a rear side portion of the platform near the blade fitting portion on the blade trailing edge side. The cooling air blow holes include a plurality of cooling holes provided in the platform. The cooling holes are arranged along the platform cooling passage on the blade dorsal side, and each hole has one end communicating with the platform cooling passage on the blade dorsal side and another end opening at an end face on the blade dorsal side of the platform.
(11) A gas turbine moving blade as mentioned in (10) above, further comprising a blade tip thinned portion provided only at a blade tip edge portion on the blade dorsal side.
In the invention as described in (1), because there is provided the recessed portion, or cut-out portion, having the smooth curved surface, in the rear end face portion of the platform near the blade fitting portion on the blade trailing edge side, a thick portion of the platform near this blade fitting portion is thinned by the recessed portion. Thus, there is eliminated a sharp thickness change between the thin blade portion and the thick platform portion, and also the mass of the platform right under the thin blade portion is reduced by the recessed portion to make the thermal capacity thereat smaller, and thus the thermal capacity difference also can be made smaller. Accordingly, the temperature difference caused by the difference in the cooling velocity during gas turbine stoppage or the like also becomes smaller, and occurrence of cracks as have been caused by the thermal stresses at the blade fitting portion can be prevented. Further, because the fillet of the blade fitting portion has a curved surface which has partially the linear portion, the fillet R is larger than that of the conventional case with regard to curvature and the rigidity of this portion is strengthened. Moreover, because the lowermost hole of the cooling air blow holes provided in the blade trailing edge has a cross sectional area larger than that of the other cooling air blow holes, the cooling effect of this portion is enhanced and the temperature difference in the blade fitting portion becomes smaller to suppress occurrence of thermal stresses, and thus cracks can be avoided.
In the invention as described in (2), because the thermal barrier coating (TBC) of the heat resistant material is applied to the blade, so that temperature lowering of the blade after stoppage of the gas turbine becomes slower, the temperature difference between the blade fitting portion and the platform becomes smaller and thus the thermal stresses are made smaller. Also, temperature lowering of the blade portion where the thicker TBC is applied becomes further slower, and the temperature difference between the blade and the platform becomes further smaller. Moreover, because of the platform portion where the thinner TBC is applied, temperature lowering of the platform at and around this portion is comparatively fast, so that the temperature difference between the blade fitting portion and the platform becomes further smaller and thus thermal stresses caused thereat are made further smaller. Also, in the invention as described in (3), because the fillet exterior of the blade fitting portion is elliptically curved, the curvature of the fillet exterior becomes large and the stress concentration in this portion can be mitigated.
In the invention as described in (4), when the gas turbine is stopped, the control unit opens the opening/closing valve for the predetermined time so that cooling air from the platform cooling air supply system may be led actively into the cooling passage of the platform, and the platform is cooled even during stoppage of the gas turbine. Hence, cooling of the platform, which is slower in temperature lowering than is the thin moving blade, is accelerated. Also, the temperature difference between the blade and the platform is made smaller to suppress occurrence of thermal stresses, and thus occurrence of cracks is prevented.
In the invention as described in (5), because the shank portion which fixes the platform is elongated in its height direction as compared with the conventional shank portion, deformation caused by thermal stresses at the connection portion of the blade and the platform is absorbed by a damping effect which results from the elongation of the shank portion, thereby mitigating the influences of thermal stresses whereby occurrence of cracks is prevented.
In the invention as described in (6), pertaining to a first stage moving blade, because there are two flow paths of the serpentine cooling passage in which the cooling air flows toward the blade leading edge side and toward the blade trailing edge side, the blade interior is cooled effectively. At the same time, because the recessed portions or cut-out portions are provided in the platform front and rear end faces near the blade fitting portions on the blade leading edge and trailing edge sides, the thick portions right under the mentioned blade fitting portions are thinned by the recessed portions. Thus, there is eliminated a sharp thickness change between the thin blade and the thick platform, and also mass of the platform in the mentioned portions is reduced to lower the thermal capacity thereat and to thereby make the thermal capacity difference smaller. Accordingly, the temperature difference caused by the difference in the cooling velocity between the blade and platform becomes smaller, and occurrence of cracks due to thermal stresses as have been caused at the connection portion of the blade and the platform is prevented. Moreover, because the platform is cooled by the cooling air flowing through the cooling passages of both side end portions, or the blade ventral and dorsal side end portions, of the platform, as well as the cooling air flowing out of the platform side end face through the cooling holes provided along the cooling passage on the blade dorsal side end portion of the platform, the blade dorsal side end portion of the platform which is exposed to high temperature combustion gas, and thus prone to be in a thermally severe state, is cooled effectively.
In the invention as described in (7), because the exterior of the two fillets on the blade leading edge and trailing edge sides has a curved surface having the combination of the linear portion and the curved portion, for example, with the linear portion being on the upper side of the fillet and the curved portion being on the lower side near the blade fitting portion, the mentioned curved surface approaches a linear surface such that the curvature of the fillet is larger than that of the fillets on the blade ventral and dorsal sides, and thereby rigidity of this portion is enhanced, occurrence of thermal stresses is suppressed, and occurrence of cracks is prevented.
In the invention as described in (8), because the blade tip thinned portion on the blade ventral side tip edge portion is eliminated as compared with the conventional case, and the blade tip thinned portion is only provided on the blade dorsal side tip edge portion, which receives especially high thermal influences, the blade tip sealing performance is at least maintained by the blade tip thinned portion on the blade dorsal side tip edge portion, such that damage of the blade tip thinned portion due to high temperature can be lessened. Also, because the plug is of a circular shape, fitting of the plug becomes facilitated and damage thereof due to high temperature is lessened.
In the invention as described in (9), because the shank portion which fixes the platform is elongated in its height direction as compared with the conventional shank portion, deformation caused by thermal stresses at the connection portion of the blade and the platform is absorbed by the damping effect which results from the elongation of the shank portion, thereby mitigating the influences of thermal stresses whereby occurrence of cracks is prevented.
In the invention as described in (10), pertaining to a second stage moving blade, because the serpentine cooling passage comprises the flow path in which the cooling air entering the central portion flows toward the blade trailing edge side, the blade interior is cooled effectively. At the same time, because the recessed portion or cut-out portion is provided in the platform rear end face near the blade fitting portion on the blade trailing edge side, the thick portion right under the mentioned blade fitting portion is thinned by the recessed portion. Thus, there is eliminated a sharp thickness change between the thin blade and the thick platform, and also mass of the platform in the mentioned portion is reduced to lower the thermal capacity thereat and to thereby make the thermal capacity difference smaller. Accordingly, the temperature difference caused by the difference in the cooling velocity between the blade and the platform becomes smaller, and occurrence of cracks due to thermal stresses as have been caused at the connection portion of the blade and the platform is prevented. Moreover, because the platform is cooled by the cooling air flowing through the cooling passages of both side end portions, or the blade ventral and dorsal side end portions, of the platform, as well as the cooling air flowing out of the platform side end face through the cooling holes provided along the cooling passage on the blade dorsal side end portion of the platform, the blade dorsal side end portion of the platform which is exposed to high temperature combustion gas, and thus prone to be in a thermally severe state, is cooled effectively.
In the invention as described in (11), because the blade tip thinned portion on the blade ventral side tip edge portion is eliminated as compared with the conventional case, and the blade tip thinned portion is only provided on the blade dorsal side tip edge portion, which receives especially high thermal influences, the blade tip sealing performance is at least maintained by the blade tip thinned portion on the blade dorsal side tip edge portion such that damage of the blade tip thinned portion due to high temperature can be lessened.